The field of the invention relates generally to devices for the treatment of Obstructive Sleep Apnea (OSA). More specifically, the invention relates to devices and methods for the treatment and resolution of the underlying obesity that causes, exacerbates, or triggers OSA. The device and methods employ objective monitoring of the metabolic rate of a patient.
Sleep related breathing disorders adversely affect an individual""s breathing during periods of sleep. Breathing disruption in sleep often results from the collapse or closing of an individual""s air passageway. OSA, as one common example of a sleep related breathing disorder, is an abnormal physical condition that affects a person""s ability to breathe properly after falling asleep. Persons suffering from sleep apnea can stop breathing for periods as short as a few seconds and as long as a few minutes.
Frequently, a patient that suffers from OSA is obese. Obesity contributes to an increase in the upper airway resistance due to deposits of adipose tissue in the upper airway, specifically, the hypopharynx. During periods of sleep, tissue in this region relaxes and blocks airflow into and out of the afflicted person""s lungs.
Typically, sleep related breathing disorders such as OSA are treated by Continuous Positive Air Pressure (CPAP) therapy. In CPAP therapy, a device that is essentially an air pump forces air into an individual""s air passageway. The CPAP device maintains sufficient pressure to keep the air passageway open during periods of sleep. The patient typically wears a masklike device that is connected to the CPAP device to provide an elevated air pressure in the patient""s upper air passageway. One such device is the ALURA Nasal CPAP System sold by Thermo Respiratory Group/Bird SensorMedics Bear, 1100 Bird Center Drive, Palm Springs, Calif. 92262. Other devices known as BiPAP (Bi-Level Positive Airway Pressure) devices operate at two positive air pressure levels. A lower pressure level is used during exhalation while a higher pressure level is used during inhalation. The BiPAP device makes it easier to exhale due to the lower pressure used during exhalation. BiPAP devices are often prescribed for individuals that require higher pressures than those present in CPAP devices.
Since OSA is so often associated with obesity, it is desirable to treat the underlying obesity condition. Generally, obesity may be resolved by the strict application of nutrition and diet control. It has been demonstrated, for example, that the measurement of resting energy expenditure (REE) by indirect calorimetry (IC) is useful in determining an individual patient""s caloric needs and monitoring the patient""s nutritional intake.
At the present time, there does not exist a comprehensive device that can monitor a patient""s REE that also delivers positive airway pressure (CPAP or BiPAP). A device combining these two functions has been elusive since there is a natural clash between the positive airflow of CPAP/BiPAP devices and the negative airflow requirement of IC devices. Accordingly, there is a need for a single device that can (1) provide positive airway pressure to a patient, and (2) monitor or measure the REE of the patient.
In a first aspect of the invention, a device for applying positive airway pressure to a patient and measuring the patient""s resting energy expenditure includes a breathing circuit having a first end and a second end. A patient interface device is coupled to one of the first and second ends. A bi-directional pump is positioned within the breathing circuit between the first end and the second end. An indirect calorimetry module is positioned within the breathing circuit. The indirect calorimetry module measures the patient""s resting energy expenditure.
In a second aspect of the invention, a device for applying positive airway pressure to a patient and measuring the patient""s resting energy expenditure includes a breathing circuit having a patient interface device connected at one end and an inlet/exhaust port at the other end of the breathing circuit. A bi-directional pump is positioned within the breathing circuit between the patient interface device and the inlet/exhaust port. An indirect calorimetry module is also positioned within the breathing circuit and adjacent to the bi-directional pump. The indirect calorimetry module includes an oxygen sensor, a carbon dioxide sensor, and a flow rate sensor. The device also includes a microprocessor for calculating the patient""s resting energy expenditure based on the concentration of oxygen, the concentration or carbon dioxide, and the flow rate within breathing circuit.
In a third aspect of the invention, a method of supplying positive airway pressure to a patient includes the steps of supplying a patient with positive airway pressure via a breathing circuit, the positive airway pressure traveling through the breathing circuit in a first direction. Next, the flow in the breathing circuit is reversed during one or more expiration breaths of a patient. The concentration of oxygen and carbon dioxide is monitored in the breathing circuit during the one or more expiration breaths. The flow rate of gas in the breathing circuit is also monitored during the one or more expiration breaths. Finally, the resting energy expenditure of the patient is calculated based on the concentration of oxygen, the concentration of carbon dioxide, and the flow rate within the breathing circuit.
It is an object of the invention to provide a device that delivers positive airway pressure to a patient that also has the capability to measure REE. The device can be used in connection with a patient""s weight reduction or weight maintenance program. The device gives objective feedback to the patient and/or health care provider about the patient""s caloric expenditure.